Accidents resulting from a loss of airplane control, sometimes referred to as airplane “upsets”, are a major cause of fatalities in the commercial aviation industry.
The following unintentional flight conditions generally describe an airplane upset: pitch attitude greater than 25 degrees nose up; pitch attitude greater than 10 degrees nose down; bank angle greater than 45 degrees; and within the foregoing parameters, but flying at airspeeds inappropriate for the conditions.
The causes of airplane upset incidents are varied, however, they can be broken down into four broad categories, namely: environmentally induced; system-anomalies induced; pilot induced; and a various combinations of the foregoing categories.
Environmentally induced airplane upsets include the following: turbulence; clear air turbulence, mountain wave turbulence, wind shear, thunderstorms, microbursts, wake turbulence, and airplane icing.
Turbulence is characterized by a large variation in an air current over a short distance. It is caused by, among other things, jet streams, convective currents, obstructions to wind flow, and wind shear. Knowledge of the various types of turbulence assists in avoiding it, and, consequently, reduces the potential for an airplane upset.
Clear air turbulence (CAT) is defined as high-level turbulence, as it is normally above 15,000 MSL (mean sea level). It is not associated with cumuliform cloudiness. CAT is almost always present near jet streams. Jet streams are dynamic, and turbulence associated with them is difficult to predict. This area of turbulence can be 100 to 300 miles long, 50 to 100 miles wide, and 2000 to 5000 feet thick.
Mountains are the greatest obstructions to wind flow. This type of turbulence is classified as “mechanical.” Lenticular clouds over mountains are a sure sign of mountain wave turbulence, but unfortunately the air may be too dry for the presence of the telltale clouds, increasing the likelihood of upsets.
Wind shear wind variations at low altitude are recognized as a serious hazard to airplanes during takeoff and approach. These variations can be caused by many differing meteorological conditions including, but not limited to, topographical, temperature inversions, sea breezes, frontal systems, strong surface winds, thunderstorms, and microbursts. Thunderstorms and microbursts are the two most violent forms of wind change.
The two basic types of thunderstorms are air mass and frontal. Air mass thunderstorms are randomly distributed in unstable air. Heated air rises to form cumulus clouds. The clouds develop in three stages: cumulus stage, mature stage, and dissipating stage. The gust front produced by the downflow and outrush of rain-cooled air can produce very turbulent air conditions.
Frontal thunderstorms are associated with weather system line fronts, converging wind, and troughs aloft. Frontal thunderstorms form in squall lines, last several hours, generate heavy rain and possibly hail, and produce strong gusty winds and possibly tornadoes. The downdraft of a typical frontal thunderstorm is large, about 1 to 5 miles in diameter. Resultant outflows may produce large changes in wind speed.
Microbursts can occur anywhere that convective weather conditions occur. Five percent of all thunderstorms produce microbursts. Downdrafts are typically only a few hundred to 3,000 feet across. The outflows are not always symmetrical. A significant airspeed increase may not occur upon entering outflows, or it may be much less than the subsequent airspeed loss experienced when exiting. Some microbursts are so severe that an aircraft cannot escape them.
Wake turbulence is a leading cause of airplane upsets that are environmentally induced. A pair of counter-rotating vortices is shed from an airplane wing, thus causing turbulence in the airplane's wake. The effect of turbulence on the aircraft is a function of airplane weight, wingspan, and speed. Vortices descend at an initial rate of 300 to 500 feet/minute for about 30 seconds. Pilots have likened a wake-turbulence encounter to be like hitting a wall. With little to no control input from the pilot, the airplane would be expelled from the wake and an airplane upset could result.
With regard to airplane icing, large degradation of airplane performance can result from the surface roughness of an extremely small amount of ice contamination. The handling characteristics and lift capability can be adversely affected. Therefore, the axiom of “keep it clean” for critical airplane surfaces continues to be a universal requirement.
System-anomalies induced airplane upsets can arise from the failure of items such as airplane systems (i.e., engines, electric, hydraulic, and flight controls), flight instruments and auto-flight systems as well as other anomalies. These types of failures can range from unrecoverable to survivable if the flight crew makes correct responses.
Airplane system failures involve the loss or degradation of one or more aircraft systems. Primary airplane systems include engines, electric, hydraulic, and flight controls. Emergency procedures are published for many systems failures. Successful resolution of a system failure involves the pilot recognizing the failure and maintaining aircraft control while executing the proper emergency procedure.
With regard to instrument failures, virtually all airplane operations manuals provide flight instrument system information that the pilot can analyze to select the correct procedural alternatives. Several accidents have pointed out that pilots are not always prepared to correctly analyze the alternatives in case of failure. The result can be catastrophic.
Auto-flight systems include autopilot, auto-throttles, and all related systems that perform automatic control of the aircraft, flight management, and guidance. The pilot community has tended to develop a great deal of confidence in these systems, which has led to complacency in some cases. Although quite reliable, failures do occur. These failures have led to airplane upsets and accidents.
Flight controls include primary flight controls (ailerons/spoilers, rudder, and elevator/stabilizer) and secondary flight controls (including trim surfaces, flaps, and speedbrakes). Flight control damage or failure can occur due to a variety of reasons including mechanical failure, bird strike, or overstress. These failures and other anomalies such as flap asymmetry, runaway trim and aileron/spoiler problems are addressed in airplane operations manuals. Airplane certification requirements ensure that pilots have sufficient information and are trained to handle these critical failures. However, it is the unexpected that can cause problems, and an accident.
With regard to pilot-induced airplane upsets, it has been known for many years that sensory inputs can be misleading to pilots, especially when pilots cannot see the horizon. To solve this problem, airplanes are equipped with flight instruments to provide the necessary information for controlling the airplane. However, a review of airplane upsets reveals that pilot inattention to, or neglect of, the airplane's performance can lead to extreme deviations from the normal flight envelope. Distractions can be very subtle, such as warning or caution lights illuminating during critical phases of flight, conflicting traffic, or radio calls during critical phases of flight. Many airplane upsets occur while the pilot is engaged in some task that takes attention away from the flight instruments.
Spatial disorientation has been a significant factor in many airplane upset accidents. The definition of spatial disorientation is the inability to correctly orient oneself with respect to the Earth's surface due to misinterpretation of the aircraft position and/or motion. We are all susceptible to sensory illusions. Pilots who perceive a conflict between bodily senses and the flight instruments and are unable to resolve the conflict are spatially disoriented. Allowed to continue, a spatial disorientation episode will likely lead to an airplane upset. Attention to flight instruments and a good cross-check are the keys to remaining spatially orientated.
The advancement of technology in today's modern airplanes has brought us flight directors, autopilots, auto-throttles, flight management systems, and ground collision avoidance systems. When used properly, this technology contributes to flight safety and reduces crew workload. Complacent and improper use of these systems is a concern. The systems can and do fail, leading to airplane upsets and accidents.
Data from the U.S. National Transportation Safety Board show that between 1993 and 2002, there were 2,131 fatalities in loss of control accidents and that some of these fatalities were attributable to airplane upsets. See Docket No. SA-531 Exhibit No. 14-M National Transportation Safety Board Washington, D.C. Flight Safety Digest, July.
Another airline industry source reports that there were twenty-two in-flight, loss-25 of-control accidents between 1999 and 2008. (See Statistical Summary of Commercial Jet Airplane Accidents, Worldwide Operations, 1959-2008) These accidents resulted in more than 1,991 fatalities.
These accident and fatality statistics suggest that pilots need training so that they are better prepared to respond to airplane upset situations.
Many commercially trained pilots do not receive training in the procedures and techniques necessary to recover from an upset. See Airplane Upset Recovery Training Aid Revision 2, available online at flightsafety.org. Military pilots, on the other hand, receive upset recovery training, but the ratio of military trained pilots to commercially trained pilots in commercial aviation continues to shift toward more commercially trained pilots.
The goal of prior art upset recovery training was, since complete avoidance of upsets was not possible, that pilots should be trained to safely recover an airplane that has been upset.
The goal of prior art upset recovery training programs was, in a classroom situation, to increase the pilot's ability to recognize and avoid upset situations and to improve the pilot's ability to recover control, if avoidance is not successful.
Most prior art upset recovery training programs are, in a classroom setting, presented in three parts: (1) the causes of airplane upsets; (2) a brief review of airplane fundamentals; and (3) airplane upset recovery techniques.
Airplane manufacturers, airlines, pilot associations, flight training organizations, and government and regulatory agencies have developed these prior art training resources.
The goal of the prior art training aid has been to increase the ability of pilots to recognize and avoid situations that can lead to airplane upsets and to improve their ability to recover control of an airplane that has exceeded the normal flight regime.
The use of simulators in prior art upset recovery training (“URT”) programs has not been well accepted because a traditional simulator cannot replicate the sustained motions and accelerations experienced in an actual upset situation. Many believe that use of a simulator creates a potential for negative learning, in that it may, because of limitations in the simulator being used, reinforce recovery techniques that may not work, and may in fact fail catastrophically, in real world conditions.
In prior art URT programs, ground-based motion simulation of aircraft has been considered using “six-post” or “hexapod” devices. (See FIG. 1.) In prior art URT programs, ground-based motion simulation of aircraft has also been considered using a Level D simulator. Level D is a simulator classification by the U.S. Federal Aviation Administration. (See FIG. 2.) Level D flight simulator devices have the following characteristics and components: (1) systems representations, switches, and controls which are required by the type design of the aircraft and by the user's approved training program; (2) systems which respond appropriately and accurately to the switches and controls of the aircraft being simulated; (3) full-scale replica of the cockpit of the aircraft being simulated; (4) correct simulation of the aerodynamic (including ground effect) and ground dynamic characteristics of the aircraft being simulated in the normal flight environment; (5) correct simulation of selected environmentally-affected aerodynamic and ground dynamic characteristics of the aircraft being simulated considering the full range of its flight envelope in all approved configurations; (6) correct and realistic simulation of the effects of environmental conditions which the aircraft might encounter; (7) control forces, dynamics, and travel which correspond to the aircraft; (8) instructor controls and seat; (9) a daylight, dusk, and night visual system with the minimum of a 75° horizontal by 30° vertical field of view for each pilot station; and (10) a motion system with at least 6 degrees of freedom. These devices are able to provide transient motion cues with little addition to the response time that a pilot senses. These devices are, however, not able to provide sustained acceleration or sustained motion cues. This means that flight fidelity is diminished in many maneuvers such as a basic coordinated turn and particularly during flight conditions that are outside the normal flight envelope. This missing fidelity does not allow training pilots to cope with vestibular and tactile illusions that routinely occur in flight.
What is needed is a method of upset recovery training that replicates the sustained motions and accelerations experienced in an actual upset condition, thereby allowing pilots to train to cope with the vestibular and tactile stresses that occur in both flight and in an upset condition.